Don't set a fast default for anything but a plain table

The fast default code added in Release 11 omitted to check that the
table a fast default was being added to was a plain table. Thus one
could be added to a foreign table, which predicably blows up. Here we
perform that check.

In addition, on the back branches, since some of these might have
escaped into the wild, if we encounter a missing value for
an attribute of something other than a plain table we ignore it.

Fixes bug #17056

Backpatch to release 11,

Reviewed by: Andres Freund, Álvaro Herrera and Tom Lane

src/backend/catalog/heap.c

@@ -2065,6 +2065,13 @@ SetAttrMissing(Oid relid, char *attname, char *value)
 	/* lock the table the attribute belongs to */
 	tablerel = heap_open(relid, AccessExclusiveLock);
 
+	/* Don't do anything unless it's a plain table */
+	if (tablerel->rd_rel->relkind != RELKIND_RELATION)
+	{
+		table_close(tablerel, AccessExclusiveLock);
+		return;
+	}
+
 	/* Lock the attribute row and get the data */
 	attrrel = heap_open(AttributeRelationId, RowExclusiveLock);
 	atttup = SearchSysCacheAttName(relid, attname);
@@ -2198,7 +2205,7 @@ StoreAttrDefault(Relation rel, AttrNumber attnum,
 		valuesAtt[Anum_pg_attribute_atthasdef - 1] = true;
 		replacesAtt[Anum_pg_attribute_atthasdef - 1] = true;
 
-		if (add_column_mode)
+		if (rel->rd_rel->relkind == RELKIND_RELATION  && add_column_mode)
 		{
 			expr2 = expression_planner(expr2);
 			estate = CreateExecutorState();

src/backend/commands/tablecmds.c

@@ -10315,10 +10315,11 @@ ATExecAlterColumnType(AlteredTableInfo *tab, Relation rel,
 
 	/*
 	 * Here we go --- change the recorded column type and collation.  (Note
-	 * heapTup is a copy of the syscache entry, so okay to scribble on.)
+	 * heapTup is a copy of the syscache entry, so okay to scribble on.) First
-	 * First fix up the missing value if any.
+	 * fix up the missing value if any. There shouldn't be any missing values
+	 * for anything except plain tables, but if there are, ignore them.
 	 */
-	if (attTup->atthasmissing)
+	if (rel->rd_rel->relkind == RELKIND_RELATION  && attTup->atthasmissing)
 	{
 		Datum       missingval;
 		bool        missingNull;

src/backend/utils/cache/relcache.c

@@ -546,6 +546,7 @@ RelationBuildTupleDesc(Relation relation)
 	{
 		Form_pg_attribute attp;
 		int			attnum;
+		bool        atthasmissing;
 
 		attp = (Form_pg_attribute) GETSTRUCT(pg_attribute_tuple);
 
@@ -559,6 +560,22 @@ RelationBuildTupleDesc(Relation relation)
 			   attp,
 			   ATTRIBUTE_FIXED_PART_SIZE);
 
+		/*
+		 * Fix atthasmissing flag - it's only for plain tables. Others
+		 * should not have missing values set, but there may be some left from
+		 * before when we placed that check, so this code defensively ignores
+		 * such values.
+		 */
+		atthasmissing = attp->atthasmissing;
+		if (relation->rd_rel->relkind != RELKIND_RELATION && atthasmissing)
+		{
+			Form_pg_attribute nattp;
+
+			atthasmissing = false;
+			nattp = TupleDescAttr(relation->rd_att, attnum - 1);
+			nattp->atthasmissing = false;
+		}
+
 		/* Update constraint/default info */
 		if (attp->attnotnull)
 			constr->has_not_null = true;
@@ -578,7 +595,7 @@ RelationBuildTupleDesc(Relation relation)
 		}
 
 		/* Likewise for a missing value */
-		if (attp->atthasmissing)
+		if (atthasmissing)
 		{
 			Datum		missingval;
 			bool		missingNull;

src/test/regress/expected/fast_default.out

@@ -797,7 +797,26 @@ SELECT * FROM t WHERE a IS NULL;
 (1 row)
 
 ROLLBACK;
+-- verify that a default set on a non-plain table doesn't set a missing
+-- value on the attribute
+CREATE FOREIGN DATA WRAPPER dummy;
+CREATE SERVER s0 FOREIGN DATA WRAPPER dummy;
+CREATE FOREIGN TABLE ft1 (c1 integer NOT NULL) SERVER s0;
+ALTER FOREIGN TABLE ft1 ADD COLUMN c8 integer DEFAULT 0;
+ALTER FOREIGN TABLE ft1 ALTER COLUMN c8 TYPE char(10);
+SELECT count(*)
+  FROM pg_attribute
+  WHERE attrelid = 'ft1'::regclass AND
+    (attmissingval IS NOT NULL OR atthasmissing);
+ count 
+-------
+     0
+(1 row)
+
 -- cleanup
+DROP FOREIGN TABLE ft1;
+DROP SERVER s0;
+DROP FOREIGN DATA WRAPPER dummy;
 DROP TABLE vtype;
 DROP TABLE vtype2;
 DROP TABLE follower;

src/test/regress/sql/fast_default.sql

@@ -524,8 +524,22 @@ SET LOCAL enable_seqscan = false;
 SELECT * FROM t WHERE a IS NULL;
 ROLLBACK;
 
+-- verify that a default set on a non-plain table doesn't set a missing
+-- value on the attribute
+CREATE FOREIGN DATA WRAPPER dummy;
+CREATE SERVER s0 FOREIGN DATA WRAPPER dummy;
+CREATE FOREIGN TABLE ft1 (c1 integer NOT NULL) SERVER s0;
+ALTER FOREIGN TABLE ft1 ADD COLUMN c8 integer DEFAULT 0;
+ALTER FOREIGN TABLE ft1 ALTER COLUMN c8 TYPE char(10);
+SELECT count(*)
+  FROM pg_attribute
+  WHERE attrelid = 'ft1'::regclass AND
+    (attmissingval IS NOT NULL OR atthasmissing);
 
 -- cleanup
+DROP FOREIGN TABLE ft1;
+DROP SERVER s0;
+DROP FOREIGN DATA WRAPPER dummy;
 DROP TABLE vtype;
 DROP TABLE vtype2;
 DROP TABLE follower;